U.S. patent application number 11/392552 was filed with the patent office on 2006-10-05 for method and apparatus for drying a fibrous material.
This patent application is currently assigned to Hauni Maschinenbau Ag. Invention is credited to Torsten Koch.
Application Number | 20060218814 11/392552 |
Document ID | / |
Family ID | 36608591 |
Filed Date | 2006-10-05 |
United States Patent
Application |
20060218814 |
Kind Code |
A1 |
Koch; Torsten |
October 5, 2006 |
Method and apparatus for drying a fibrous material
Abstract
The application concerns a method for drying a fibrous material
by means of a process gas stream flowing through a pipe, including
heating the process gas flowing through the pipe by means of a
heater with controllable heating power, and conducting a portion of
the process gas stream through a bypass pipe bypassing the heater,
wherein the ratio of mass flows of process gas flowing through the
heater and through the bypass pipe is adjustable, and is
distinguished by the fact that the heating power of the heater is
controlled according to the set ratio of mass flows of process gas
through the heater and through the bypass pipe. The application
further concerns a corresponding drying apparatus.
Inventors: |
Koch; Torsten; (Bad
Oldesloe, DE) |
Correspondence
Address: |
VENABLE LLP
P.O. BOX 34385
WASHINGTON
DC
20045-9998
US
|
Assignee: |
Hauni Maschinenbau Ag
Hamburg
DE
|
Family ID: |
36608591 |
Appl. No.: |
11/392552 |
Filed: |
March 30, 2006 |
Current U.S.
Class: |
34/360 ;
34/553 |
Current CPC
Class: |
A24B 3/04 20130101; F23N
1/082 20130101; F23N 2225/21 20200101; F26B 17/101 20130101; F26B
21/10 20130101; F26B 2200/22 20130101 |
Class at
Publication: |
034/360 ;
034/553 |
International
Class: |
F26B 3/08 20060101
F26B003/08; F26B 19/00 20060101 F26B019/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 1, 2005 |
DE |
10 2005 015 781.5 |
Claims
1. Method for drying a fibrous material by means of a process gas
stream flowing through a pipe, including heating the process gas
flowing through the pipe by means of a heater with controllable
heating power, and conducting a portion of the process gas stream
through a bypass pipe bypassing the heater, wherein the ratio of
mass flows of process gas flowing through the heater and through
the bypass pipe being adjustable, characterised in that the heating
power of the heater is controlled according to the set ratio of
mass flows of process gas through the heater and through the bypass
pipe.
2. Method according to claim 1, characterised in that the heating
power of the heater is regulated as a function of the temperature
of the process gas leaving the heater.
3. Method according to claim 2, characterised in that regulation of
the heating power of the heater is affected by the set mass flow of
process gas through the heater.
4. Method according to claim 2, characterised in that the setpoint
for regulation of the heating power of the heater is changed
according to the set mass flow of process gas through the
heater.
5. Method according to claim 1, characterised in that the heating
power of the heater is reduced as a result of a reduction of the
mass flow of process gas flowing through the heater.
6. Method according to claim 1, characterised in that the heating
power of the heater is increased as a result of an increase of the
mass flow of process gas flowing through the heater.
7. Method according to claim 5, characterised in that the lower or
higher the mass flow of process gas flowing through the heater, the
greater the decrease or increase of heating power of the
heater.
8. Method according to claim 1, characterised in that the setpoint
superimposing for control of the heating power of the heater sets
in when the mass flows of process gas deviate from a mean value by
more than 20%, preferably by more than 13%.
9. Method according to claim 1, characterised in that the ratio of
mass flows of process gas through the heater and through the bypass
pipe is regulated as a function of the temperature of the process
gas used for drying.
10. Method according to claim 1, characterised in that the heater
includes a heat exchanger arranged in the pipe.
11. Method according to claim 10, characterised in that the heating
power of the heater is controlled in such a way that variations of
the wall temperature in the heat exchanger remain as small as
possible as a result of a variation in the mass flow of process gas
flowing through the heater.
12. Apparatus for drying a fibrous material by means of a process
gas stream flowing through a pipe, with a heater installed in the
pipe for heating the process gas flowing through the pipe, wherein
the heating power of the heater being controllable, a bypass pipe
bypassing the heater for a portion of the process gas stream, and a
controllable device for adjusting the ratio of mass flows of
process gas flowing through the heater and through the bypass pipe,
characterised in that the apparatus has control means for
controlling the heating power of the heater according to the
adjusted ratio of mass flows of process gas through the heater and
through the bypass pipe.
13. Apparatus according to claim 12, characterised in that a
regulating circuit is provided for regulating the heating power of
the heater to a constant temperature of the process gas leaving the
heater.
14. Apparatus according to claim 13, characterised in that the
control means is adapted to affect the regulating circuit.
15. Apparatus according to claim 13, characterised in that the
control means is adapted to vary the setpoint of the regulating
circuit according to the adjusted mass flow of process gas through
the heater.
16. Apparatus according to claim 12, characterised in that the
heater has a heat exchanger arranged in the pipe.
17. Apparatus according to claim 12, characterised in that the
device for adjusting the ratio of mass flows of process gas flowing
through the heater and through the bypass pipe includes at least
one adjustable valve.
18. Apparatus according to claim 17, characterised in that control
of the heating power of the heater is affected as a function of the
position of the valve.
19. Apparatus according to claim 12, characterised in that a
regulating circuit is provided for regulating the ratio of mass
flows of process gas through the heater and through the bypass pipe
as a function of the temperature of the process gas used for
drying.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the priority of German Patent
Application No. 10 2005 015 781.5 filed Apr. 1, 2005, the subject
matter of which is incorporated herein by reference. The disclosure
of all U.S. and foreign patents and patent applications mentioned
below are also incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The invention concerns a method and an apparatus for drying
a fibrous material according to the preamble of claims 1 and
12.
[0003] Such an apparatus is known from DE 33 05 670 C2, which
comprises a regulating bypass and a second parallel standby bypass.
The mass flow of process gas flowing through the regulating bypass
is regulated as a function of the temperature of the load. The fuel
and the combustion air for the burner are regulated as a function
of the temperature of the flue gases produced by the burner.
Ballast air for the burner is regulated as a function of the
temperature of the process gas stream behind the heat exchanger. A
reduction of the mass flow of process gas flowing through the
regulating bypass leads to an increase in the wall temperature in
the heat exchanger and therefore, on account of the high inertia of
the heat exchanger, a significant delay in regulation of the
temperature of the process gas stream, and hence a reduction of
efficiency of the drying apparatus.
SUMMARY OF THE INVENTION
[0004] It is the object of the present invention to provide a
drying method and a drying apparatus which allow quick regulation
and efficient operation.
[0005] The invention achieves this object with the features of
claims 1 and 12. Control of the heating power of the heater
according to the invention permits adaptation in particular to the
variable mass flow of process gas through the heater. The invention
realizes that variations in the mass flow of process gas through
the heater can lengthen the regulation times in relation to the
process gas temperature, and that this can be counteracted by
control of the heating power of the burner.
[0006] Control does not necessarily mean unregulated control, but
can also be regulation. Control is therefore to be understood
within the scope of this application as control and/or regulation.
Control of the heating power can take place differently, for
example by control of the combustion air supply, the fuel supply
and/or ballast air.
[0007] Particularly useful is application of the invention to a
heater with indirect heating, in particular by means of a heat
exchanger which reacts particularly inertly on account of the high
mass.
[0008] In a preferred embodiment, the setpoint for a preferred
regulation of the heating power of the heater as a function of the
temperature of the process gas leaving the heater is varied
depending on the set mass flow of process gas through the
heater.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Further advantageous characteristics are apparent from the
subsidiary claims and the following description of advantageous
embodiments with reference to the attached drawing. It shows:
[0010] FIG. 1: a schematic view of a drying apparatus for a tobacco
product.
DETAILED DESCRIPTION OF THE INVENTION
[0011] The drying apparatus shown in FIG. 1 includes a tubular
flash dryer 10 through which hot process gas flows with or without
vapour fraction, in particular hot air or hot steam (superheated
steam) with a temperature of between 130.degree. C. and 500.degree.
C. The flash dryer 10 is part of a pipe circuit through which the
process gas flows in the arrow direction. The flash dryer 10
comprises a product inlet 11 for the tobacco 12 to be dried. The
tobacco 12 is transported by the process gas stream and, in the
process, dried in the flash dryer 10. The dried tobacco is
separated by means of the separator 13 from the hot gas which is
delivered via pipes 14 to 16 via a compressor 17 to a heat
exchanger 18. By means of the heat exchanger 18, the process gas is
heated to the desired drying temperature in order to recycle the
heat extracted by the drying process. For this purpose heat is
delivered to the heat exchanger 18 by means of a combustion gas
stream 32 produced by a burner 31. The heated process gas is passed
via the supply pipe 19 to the flash dryer 10.
[0012] Parallel to the heat exchanger 18 is provided a bypass pipe
26 with a flow resistance 25, for example, a throttle, for a
portion of the process gas stream. The proportion of the process
gas stream flowing through the heat exchanger 18 or bypass pipe 26
is adjustable by means of a valve 22 arranged in the hot pipe 16 or
a valve 23 arranged in the bypass pipe 26. The valves 22, 23 are
each adjustable between a nearly closed position (for example, 10%
mass flow of gas) and a nearly fully open position (for example,
90% mass flow of gas). The range of adjustment can also be between
20% and 80% of the total mass flow of gas. The valves 22 and 23 can
be connected to each other, for example, mechanically with a
connecting means 24, in such a way that opening of one valve
automatically causes closing of the other valve and vice versa
(double valve). However, the invention is not by any means
restricted to this. The ratio of the mass flows of process gas can
also be adjustable only by means of a valve 22 arranged in the hot
pipe 16, only by means of a valve 23 arranged in the bypass pipe
26, by means of two independently adjustable valves 22, 23 or
otherwise.
[0013] By adjustment of the valves 22, 23, different mixture ratios
can be set between the relatively cool return process gas flowing
through the return pipe 15, 16 and the hot process gas heated by
the heat exchanger 18. If, for instance, the process gas
temperature in the return pipe 14, 15 is 140.degree. C. and the
temperature of the hot process gas in pipe section 21, which is
heated by the heat exchanger 18, is 260.degree. C., then by varying
the position of the valves 22, 23 the operating temperature in the
supply pipe 19 can in principle be adjusted within a range of
between 152.degree. C. (10% mass flow of gas through the heat
exchanger 18 and 90% mass flow of gas through the bypass pipe 26)
and 248.degree. C. (90% mass flow of gas through the heat exchanger
18 and 10% mass flow of gas through the bypass pipe 26).
[0014] The position of the valves 22, 23 is regulated by means of a
first regulating member 27 in such a way that the temperature in
the supply pipe 19 measured with a first temperature sensor 28 has
the setpoint operating temperature set via the setpoint input 29.
As temperature changes rapidly by mixing of the heated process gas
stream and the cooled process gas stream, this first regulating
circuit involves rapid temperature regulation.
[0015] If now, for example, the throughflow rate through the heat
exchanger 18 is lowered by corresponding adjustment of the valves
22, 23 in order to lower the operating temperature of the process
gas in the supply pipe 19, the wall temperature of the pipes in the
flow heater and hence also the temperature of the process gas
leaving the heat exchanger 18 rises. This effect runs counter to
the desired lowering of the operating temperature of the process
gas and so impairs regulation of the operating temperature of the
process gas by means of the first regulating circuit described.
Preferably, therefore, a second regulating circuit with a second
regulating device 30 is provided, with which the heating power of
the burner 31 is regulated so that the temperature in the pipe 21
behind the heat exchanger 18, which is measured with a second
temperature sensor 33, is kept constant, namely at the setpoint
temperature set via the corresponding setpoint input 34, for
example, 260.degree. C. In the above example in which the
throughflow rate through the heat exchanger 18 is lowered by
corresponding adjustment of the valves 22, 23, regulation of the
second regulating circuit leads to relatively rapid lowering of the
burner power. Thus the temperature variations in the heat
exchanger, in particular the wall temperature of the heat exchanger
pipes, can be kept almost constant, so that the corresponding
regulation in the second regulating circuit reacts rapidly.
[0016] To extend the regulating range and to reduce the regulation
time in the second regulating circuit, the setpoint for the second
regulating member 30 is varied according to the position of the
valves 22, 23. In the example of FIG. 1 this is done by means of a
separate adding member 35 which adds an original setpoint signal 36
to a signal 37 dependent on the position of the valves 22, 23
(setpoint superimposing).
[0017] The manner of operation of setpoint superimposing will be
illustrated by an example. Here the process gas temperature in the
return pipe 14, 15 is 140.degree. C. and the temperature of the hot
process gas in pipe section 21, which is heated by the heat
exchanger 18, is first regulated by means of the second regulating
circuit to a setpoint of 2600C. The position of the valves 22, 23
is adjusted in such a way that 50% of the mass flow of process gas
flows through the heat exchanger 18 and 50% through the bypass pipe
26. The operating temperature of the process gas in the supply pipe
19 is therefore first regulated to 200.degree. C. If now a
reduction of the operating temperature in the supply pipe 19 to
below 200.degree. C. is to be effected, as described above the
throughflow rate through the heat exchanger 18 is lowered by
corresponding adjustment of the valves 22, 23 by means of the first
regulating circuit. If now the mass flow of process gas through the
heat exchanger 18 drops below a certain value, preferably below 30%
of the total mass flow of process gas, further preferably already
below 37% of the total mass flow of process gas, the original
setpoint of 260.degree. C. for the second regulating member 30 is
lowered by superimposing of a corresponding signal 37, whereby the
heating power of the burner 31 is lowered immediately. As a result,
therefore, the required reduction of the heating power of the
burner 31 will take place very rapidly after adjustment of the mass
flow of process gas through the heat exchanger 18, in particular
considerably more rapidly than by the second regulating circuit on
its own. A change of temperature of the walls of the heat exchanger
is thus prevented in advance. In other words, it is the aim of
setpoint superimposing to keep the wall temperature on the pipes in
the heat exchanger as constant as possible. In general, the
regulation time can be considerably shortened by this means.
[0018] The reduction of the heating power of the burner 31 then
acts towards a reduction of the operating temperature of the
process gas in the supply pipe 19, which, on account of the first
regulating circuit, causes an adjustment of the valves 22, 23 in
order to increase the mass flow of process gas through the heat
exchanger 18 again. On account of the counteracting operation of
the first and second regulating circuits, the valves are set back
from their extreme positions again towards a position in an optimum
medium operating range, for example, corresponding to .+-.20%,
preferably .+-.13% of the total mass flow of process mass through
the heat exchanger 18, around an average value of 50%, for example.
In this operating range the flow conditions in the heat exchanger
18 are approximately constant and allow reliable and efficient
regulation. Further, on account of the counteract operation of the
first and second regulating circuits, a shortening of the
regulation time can be achieved.
[0019] Preferably, the lower the mass flow of process gas flowing
through the heat exchanger 18 is in proportion to the total mass
flow of process gas, the more the setpoint is lowered. This can be
done linearly, for example, the invention by no means being
restricted to this. Particularly preferred is a setpoint
superimposing function which is selected or determined empirically
with a view to maximum-speed counterregulation to the first
regulator 27, 28.
[0020] What has been stated above can be transferred
correspondingly to the case of an increase in operating temperature
of the process gas in the supply pipe 19.
[0021] Other rearrangements of the described setpoint superimposing
are possible. For example, a programmable control device which
controls the valves 22, 23 and in which the current position of the
valves 22, 23 is stored can generate a corresponding setpoint
signal and send it to the setpoint input 34 of the second
regulating member 30, without a separate adding member 35 being
required for this.
[0022] The invention has been described in detail with respect to
preferred embodiments, and it will now be apparent from the
foregoing to those skilled in the art, that changes and
modifications may be made without departing from the invention in
its broader aspects, and the invention, therefore, as defined in
the appended claims, is intended to cover all such changes and
modifications that fall within the true spirit of the
invention.
* * * * *